The present invention relates to automatic tire inflation systems and more specifically to a method and apparatus for controlling the inflation of tires on an agricultural implement.
Soil is made up of soil particles, water, and air. The spaces between soil particles are called pore spaces. Soil compaction occurs when soil particles are forced closer together so that pore space is reduced. Soil structure impacts the ability of soil to absorb and conduct water, nutrients, and air necessary for plant root growth activity. It is important that the soil structure is not excessively compacted. Soil compaction impacts water infiltration, water drainage, the exchange of gases within soil and soil strength. Soil compaction can cause erosion and water runoff.
Soil compaction's effect on crop growth and yield depends on the type of crop as well as the environmental conditions. When conditions are dry, some soil compaction is good for crop growth but too much compaction tends to cause decreased root growth. When conditions are wet, any soil compaction usually decreases crop growth and yield. Additionally, when conditions are wet, soil compaction decreases soil aeration which results in de-nitrification. Soil compaction can also cause nitrogen and potassium deficiencies and may increase risk of crop disease.
Deep tilling is used to de-compact soil. For various reasons known in the art, it is often advantageous to minimize tillage. This extra operation requires the producer to spend more money for fuel and labor. In addition, deep tilling typically decreases surface residue which results in less protection of the soil against soil and wind erosion. Deep tillage also causes a rougher soil profile which in turn causes excessive implement frame bounce during movement through a field for subsequent field operations. Implement frame bounce negatively impacts bale quality in hay equipment and seed depth consistency and uniform seed spacing during the planting operation. In order to reduce tillage requirements it is important to minimize compaction as much as possible.
Agricultural vehicle traffic is one of the major causes of soil compaction. Agricultural work vehicles and implements have become larger and heavier in recent years. The increase in weight of the vehicles and implements has increased the level of soil compaction that occurs within fields which in turn has reduced crop growth and yield. To minimize compaction due to vehicle traffic, in some cases tracks have been added to vehicles so that the weight of the vehicles can be distributed over wider areas. Unfortunately tracks are relatively expensive when compared to tires and can slow down operation, two shortcomings that render tracks unsuitable for many applications.
Another solution to minimize vehicle compaction has been to increase tire size and, more specifically, to increase tire width to minimize the contact pressure that the tires exert on the soil. Compaction of properly inflated large (e.g., wide) tires is comparable to compaction associated with tracks.
One other way to reduce vehicle compaction is to adjust tire pressure as a function of load on the tires. To this end, to reduce compaction, tire pressure can be reduced by letting air out of a tire which causes vehicle weight to be distributed over a larger area (i.e., the area of the portion of the tire that contacts the ground below the vehicle. Tire inflation can also be regulated to control wheel slip and to increase overall ride smoothness. A typical tire inflation system includes a controller, a compressor and a valve where the controller controls the compressor to increase tire pressure when desired and controls the valve to decrease pressure.
In at least some cases tire inflation systems have been designed that control a prime mover vehicle's tire pressure based on a draft load on a drawbar or hitch, ballast weight of the vehicle, vehicle operating speed and tire speed. Here, typically, as tire load is increases, the controller controls the compressor to increase tire pressure.
While known central tire inflation systems minimize compaction caused by prime mover vehicles such as tractors, known systems fail to eliminate or minimize compaction caused by and bounce associated with implements that are pulled by prime movers.